The Orion Bar (see Fig. REF , bottom panel) is a bright filament of the Orion molecular cloud, a site located at 414 pc [1]} that is undergoing massive star-formation. The bar is illuminated by the O7-type star \(\theta ^1\)  Ori C, the most massive member of the Trapezium young stellar cluster,
at the heart
of the Orion Nebula [2]}. The intense ionizing radiation and strong winds from \(\theta \)  Ori C power and shape the nebula [3]}, [4]}, a blister H ii region that is eating its way into the background parental cloud Orion Molecular Cloud (OMC). The incident UV radiation field is (1-3) \(\times \) 10\(^4\) times the mean
interstellar field [5]}. The first PDR layers are predominantly neutral and atomic: [H] \(>\)  [H\(_2\) ] \(\gg \)  [H\(^+\) ]. They display a wealth of near-infrared (NIR) atomic lines from low ionization potential elements
[6]}.
Gas is mainly heated by photoelectrons ejected from small grains and it is mostly cooled by the FIR [C ii] 158 \(\mu \) m and [O i] 63 \(\mu \) m fine-structure lines [7]}, [8]}, [9]}, [10]}.
The observed narrow (\(\Delta v\)  = 2–3 km s\(^{-1}\)) carbon and sulfur radio recombination lines also arise from these layers (not from
the H ii region) and provide a measure of the electron density in the PDR
[11]}, [12]}, [13]}.
The atomic PDR zone also hosts
the peak of the mid-infrared (MIR) polycyclic aromatic hydrocarbons (PAH) emission [14]}, [15]}, [7]}, [17]}, [18]}, which has led to numerous studies on dust in the Orion Bar. Indeed, based on ISO spectroscopy with the SWS spectrograph of the Orion Bar, [19]} showed that the variations in the spectral features in the \(6-9\)  \(\mu \) m spectral range (emission bands at \(6.0\) , \(6.2\) , \(6.6\) , \(7.0\) , \(7.7\) , \(8.3\) , and \(8.6\)  \(\mu \) m) are linked to variations
in the local physical conditions but also with both formation and evolution processes associated with PAHs. From imaging and spectroscopic observations with ISOCAM (\(5-16\)  \(\mu \) m), [20]} showed that at the illuminated edge of the Orion Bar, there is a systematic decrease in the intensity of the aromatic features (especially at \(7.7\)  \(\mu \) m) relative to the continuum inside the shielded molecular regions compared to the photo-dissociated and photo-ionised regions. Later, [21]} showed that a decrease in the PAH abundance together with an increase in the larger grain emissivity, fits the Spitzer and Herschel observations of the Orion Bar well. This can be explained via the scenario of PAHs being photodestroyed or coagulating onto the surface of larger grains, thus increasing their emissivity. Mid-IR photometry with SOFIA of the Orion Bar and the Orion HII region [22]} requires coagulated grains to explain the decrease by a factor of 5 to 10 of the UV and infrared dust opacities from the diffuse ISM to these PDRs. Using SOFIA, Spitzer, UKIRT, and ISO observations together with the dust destruction model SHIVA [23]}, [24]} showed that small PAHs (\(N_{\mathrm {C}}<60\) ) are most likely destroyed.
